1. Field of the Invention
The present invention relates to an ink jet ink, an ink jet recording method, and an ink cartridge.
2. Description of the Related Art
In conventional cases, a dye that can be dissolved in an aqueous medium in ink for use in ink jet recording has been mainly used as a coloring material in the ink; in recent years, investigations on the use of a pigment have been underway from the viewpoints of, for example, the light fastness and water resistance of an image. Further, investigations have been underway on the use of various polymers as a dispersant for dispersing a pigment and an additive for improving scratch resistance or marker resistance.
In each of Japanese Patent Application Laid-Open No. 2000-169771 and Japanese Patent Application Laid-Open No. 2001-40256, there is proposed an ink jet ink containing a polymer having a star structure (star polymer).
However, an ink jet ink which uses a star polymer as a dispersion polymer for a pigment to provide an image having high colorability and excellent bleeding resistance and which can maintain such excellent characteristics even after long-term storage has been heretofore absent.
An ink using a star polymer specifically described in Japanese Patent Application Laid-Open No. 2000-169771 has been unable to provide sufficient optical density and sufficient character quality. In addition, from the star polymer described in Japanese Patent Application Laid-Open No. 2000-169771, a central compound cannot be obtained by isolating a central skeleton and the star polymer has no copolymer chain of a structure necessary for turning the polymer into a dispersion polymer. Further, reactive functional groups are crosslinked upon synthesis of the star polymer, so the central skeleton of the star polymer becomes bulky. As a result, the adsorption of the polymer to the surface of a pigment is hardly performed upon dispersion of the pigment. In addition, in the synthesis method described in Japanese Patent Application Laid-Open No. 2000-169771, the number of copolymer chains of which one molecule of the star polymer is formed cannot be controlled so that the star polymer has desired characteristics. Therefore, the molecular weight distribution of the polymer becomes broad. Of the star polymers synthesized as described above, a polymer which has a low molecular weight acts as a penetrating agent for ink on a recording medium, and high optical density is hard to obtain. In addition, a high-molecular-weight polymer out of such polymers adsorbs to the pigment, but a steric hindrance repulsive force acts between the molecules of the polymer, and the repulsive force may lead to a reduction in aggregating performance of the pigment. Accordingly, there still exists a problem to be solved in order that the star polymer may be used as a dispersion polymer.
An ink using a star polymer specifically described in Japanese Patent Application Laid-Open No. 2001-40256 has been unable to provide sufficient optical density and sufficient character quality. Further, in the invention described in Japanese Patent Application Laid-Open No. 2001-40256, the star polymer is not used as a dispersion polymer, and the main purpose of the invention is to improve the fixing performance (scratch resistance or marker resistance) of the ink through the addition of the star polymer. In other words, the star polymer described in Japanese Patent Application Laid-Open No. 2001-40256 does not function as a dispersion polymer for a pigment either.
Therefore, an object of the present invention is to provide an ink jet ink being capable of achieving both high colorability and excellent bleeding resistance of an image and having excellent storage stability. Another object of the present invention is to provide an ink jet recording method and an ink cartridge each using the ink jet ink.